Participants: 8029 women ≥ 65 years of age (median 72 y, 98% Caucasian) who were participating
in a study about osteoporotic fractures and had complete bioelectric impedance measurements.
Women with bilateral hip replacement or who were unable to walk were excluded.

Main results

For all 5 measures, a U-shaped pattern was observed for the association between body
composition and mortality, with the highest mortality rates in the lowest and highest
quintiles. For body mass index, fat mass, and percentage body fat, women in the middle
2 or 3 quintiles had lower mortality rates than those in the lowest quintile; rates
in the highest quintile were not increased (Table). For lean mass and waist girth,
mortality rates in the 4 upper quintiles did not differ from those in the lowest quintile
(Table).

Conclusions

In women ≥ 65 years of age, those with the highest values for measures of body
composition did not have increased risk for mortality compared with women with the
lowest values. Women in the intermediate ranges (e.g., BMI 23.4 to 29.8 kg/m2) had reduced mortality compared with the leanest women.

Source of funding: Bone and Musculoskeletal Diseases Training Grant, National Institutes
of Health.

Commentary

Similar to several other studies, Dolan and colleagues, using carefully collected
longitudinal data from the Study of Osteoporotic Fractures (SOF), reported a U-shaped
relation between BMI (and other measures of body composition) and risk for death (i.e.,
risk for dying was greatest among the thinnest women and the most obese women). This
relation persisted regardless of the measure of body composition analyzed and despite
adjustment for confounders, including hypertension and diabetes, and the exclusion
of smokers or women who died within 2 years of enrollment. These findings differ from
those of other recent, very large studies that showed linear associations between
BMI or waist circumference, an indicator of central adiposity, and mortality (1, 2). These study samples were different (American men and Chinese women 40 to 70 y of
age, respectively) from those of the Dolan study. Because of the conflicting reports,
it is not possible to conclude whether the true, unconfounded, and unbiased relation
between body weight and all-cause mortality is linear or U-shaped. However, it is
useful to note that, across studies, the relation between obesity and mortality is
weaker among the elderly (e.g., SOF participants whose median age was 72 y) and the
relation of overweight to mortality is weaker than the relation of obesity to mortality.

What is undisputed, however, is that the prevalence of obesity in the United States
has increased dramatically over the past 40 years: Approximately 1 of every 3 American
adults is now obese (defined as BMI ≥ 30). Because obesity has been associated
in many studies with increased risk for dyslipidemia, hypertension, diabetes, cardiovascular
disease, and some types of cancer, and in a recent meta-analysis of 26 studies, with
a 22% increased risk for all-cause mortality (3), this secular trend is a cause of great public health concern. For clinicians, focusing
efforts on patients at greatest risk for weight-related morbidity and mortality remains
of paramount importance. Regardless of whether the U-shaped relation is the consequence
of residual confounding from preexisting illness or such factors as smoking (and hence
truly linear) or accurately represents an unconfounded relation (perhaps secondary
to lower energy reserves placing the thinnest persons at increased risk at times of
great biological stress), our clinical advice to eat a prudent diet, remain physically
active, and adopt a healthy lifestyle should remain the same.